RFC: rebase inconsistency in 2.18 -- course of action?

new file mode 100755
index 0000000000..8f832957fc
@@ -0,0 +1,105 @@
+#!/bin/sh
+
+test_description='git rebase + directory rename tests'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-rebase.sh
+
+test_expect_success 'setup testcase' '
+	test_create_repo dir-rename &&
+	(
+		cd dir-rename &&
+
+		mkdir x &&
+		test_seq  1 10 >x/a &&
+		test_seq 11 20 >x/b &&
+		test_seq 21 30 >x/c &&
+		test_write_lines a b c d e f g h i >l &&
+		git add x l &&
+		git commit -m "Initial" &&
+
+		git branch O &&
+		git branch A &&
+		git branch B &&
+
+		git checkout A &&
+		git mv x y &&
+		git mv l letters &&
+		git commit -m "Rename x to y, l to letters" &&
+
+		git checkout B &&
+		echo j >>l &&
+		test_seq 31 40 >x/d &&
+		git add l x/d &&
+		git commit -m "Modify l, add x/d"
+	)
+'
+
+test_expect_success 'rebase --interactive: directory rename detected' '
+	(
+		cd dir-rename &&
+
+		git checkout B^0 &&
+
+		set_fake_editor &&
+		FAKE_LINES="1" git rebase --interactive A &&
+
+		git ls-files -s >out &&
+		test_line_count = 5 out &&
+
+		test_path_is_file y/d &&
+		test_path_is_missing x/d
+	)
+'
+
+test_expect_failure 'rebase (am): directory rename detected' '
+	(
+		cd dir-rename &&
+
+		git checkout B^0 &&
+
+		git rebase A &&
+
+		git ls-files -s >out &&
+		test_line_count = 5 out &&
+
+		test_path_is_file y/d &&
+		test_path_is_missing x/d
+	)
+'
+
+test_expect_success 'rebase --merge: directory rename detected' '
+	(
+		cd dir-rename &&
+
+		git checkout B^0 &&
+
+		git rebase --merge A &&
+
+		git ls-files -s >out &&
+		test_line_count = 5 out &&
+
+		test_path_is_file y/d &&
+		test_path_is_missing x/d
+	)
+'
+
+test_expect_failure 'am: directory rename detected' '
+	(
+		cd dir-rename &&
+
+		git checkout A^0 &&
+
+		git format-patch -1 B &&
+
+		git am --3way 0001*.patch &&
+
+		git ls-files -s >out &&
+		test_line_count = 5 out &&
+
+		test_path_is_file y/d &&
+		test_path_is_missing x/d
+	)
+'
+
+test_done

index 7a48236e87..9b2a274c71 100755
@@ -113,7 +113,7 @@ test_expect_success 'git rebase -m' '
 test_expect_success 'git rebase -m --skip' '
 	git reset --hard D &&
 	clear_hook_input &&
-	test_must_fail git rebase --onto A B &&
+	test_must_fail git rebase -m --onto A B &&
 	test_must_fail git rebase --skip &&
 	echo D > foo &&
 	git add foo &&

index cf4c042214..aa2f2f0872 100644
@@ -71,7 +71,7 @@ call_merge () {
 	test -z "$strategy" && strategy=recursive
 	# If cmt doesn't have a parent, don't include it as a base
 	base=$(git rev-parse --verify --quiet $cmt^)
-	eval 'git-merge-$strategy' $strategy_opts $base ' -- "$hd" "$cmt"'
+	eval 'git merge-$strategy' $strategy_opts $base ' -- "$hd" "$cmt"'
 	rv=$?
 	case "$rv" in
 	0)

@@ -88,7 +88,7 @@ call_merge () {
 		;;
 	*)
 		die "Unknown exit code ($rv) from command:" \
-			"git-merge-$strategy $cmt^ -- HEAD $cmt"
+			"git merge-$strategy $cmt^ -- HEAD $cmt"
 		;;
 	esac
 }

index cf4c042214..aa2f2f0872 100644
@@ -71,7 +71,7 @@ call_merge () {
 	test -z "$strategy" && strategy=recursive
 	# If cmt doesn't have a parent, don't include it as a base
 	base=$(git rev-parse --verify --quiet $cmt^)
-	eval 'git-merge-$strategy' $strategy_opts $base ' -- "$hd" "$cmt"'
+	eval 'git merge-$strategy' $strategy_opts $base ' -- "$hd" "$cmt"'
 	rv=$?
 	case "$rv" in
 	0)

@@ -88,7 +88,7 @@ call_merge () {
 		;;
 	*)
 		die "Unknown exit code ($rv) from command:" \
-			"git-merge-$strategy $cmt^ -- HEAD $cmt"
+			"git merge-$strategy $cmt^ -- HEAD $cmt"
 		;;
 	esac
 }

new file mode 100755
index 0000000000..04cdae921b
@@ -0,0 +1,69 @@
+#!/bin/sh
+
+test_description='test if rebase detects and aborts on incompatible options'
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_seq 2 9 >foo &&
+	git add foo &&
+	git commit -m orig &&
+
+	git branch A &&
+	git branch B &&
+
+	git checkout A &&
+	test_seq 1 9 >foo &&
+	git add foo &&
+	git commit -m A &&
+
+	git checkout B &&
+	# This is indented with HT SP HT.
+	echo "	 	foo();" >>foo &&
+	git add foo &&
+	git commit -m B
+'
+
+#
+# Rebase has lots of useful options like --whitepsace=fix, which are
+# actually all built in terms of flags to git-am.  Since neither
+# --merge nor --interactive (nor any options that imply those two) use
+# git-am, using them together will result in flags like --whitespace=fix
+# being ignored.  Make sure rebase warns the user and aborts instead.
+#
+
+test_run_rebase () {
+	opt=$1
+	shift
+	test_expect_failure "$opt incompatible with --merge" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --merge A
+	"
+
+	test_expect_failure "$opt incompatible with --strategy=ours" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --strategy=ours A
+	"
+
+	test_expect_failure "$opt incompatible with --strategy-option=ours" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --strategy=ours A
+	"
+
+	test_expect_failure "$opt incompatible with --interactive" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --interactive A
+	"
+
+	test_expect_failure "$opt incompatible with --exec" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --exec 'true' A
+	"
+
+}
+
+test_run_rebase --whitespace=fix
+test_run_rebase --ignore-whitespace
+test_run_rebase --committer-date-is-author-date
+test_run_rebase -C4
+
+test_done

index 0e20a66e73..451252c173 100644
@@ -243,6 +243,10 @@ leave out at most one of A and B, in which case it defaults to HEAD.
 --keep-empty::
 	Keep the commits that do not change anything from its
 	parents in the result.
++
+This uses the `--interactive` machinery internally, and as such,
+anything that is incompatible with --interactive is incompatible
+with this option.
 
 --allow-empty-message::
 	By default, rebasing commits with an empty message will fail.

@@ -324,6 +328,8 @@ which makes little sense.
 	and after each change.  When fewer lines of surrounding
 	context exist they all must match.  By default no context is
 	ever ignored.
+	Incompatible with the --merge and --interactive options, or
+	anything that implies those options or their machinery.
 
 -f::
 --force-rebase::

@@ -355,13 +361,15 @@ default is `--no-fork-point`, otherwise the default is `--fork-point`.
 --whitespace=<option>::
 	These flag are passed to the 'git apply' program
 	(see linkgit:git-apply[1]) that applies the patch.
-	Incompatible with the --interactive option.
+	Incompatible with the --merge and --interactive options, or
+	anything that implies those options or their machinery.
 
 --committer-date-is-author-date::
 --ignore-date::
 	These flags are passed to 'git am' to easily change the dates
 	of the rebased commits (see linkgit:git-am[1]).
-	Incompatible with the --interactive option.
+	Incompatible with the --merge and --interactive options, or
+	anything that implies those options or their machinery.
 
 --signoff::
 	Add a Signed-off-by: trailer to all the rebased commits. Note

@@ -400,6 +408,9 @@ The `--rebase-merges` mode is similar in spirit to `--preserve-merges`, but
 in contrast to that option works well in interactive rebases: commits can be
 reordered, inserted and dropped at will.
 +
+This uses the `--interactive` machinery internally, but it can be run
+without an explicit `--interactive`.
++
 It is currently only possible to recreate the merge commits using the
 `recursive` merge strategy; Different merge strategies can be used only via
 explicit `exec git merge -s <strategy> [...]` commands.

index 40be59ecc4..f1dbecba18 100755
@@ -503,6 +503,23 @@ then
 	git_format_patch_opt="$git_format_patch_opt --progress"
 fi
 
+if test -n "$git_am_opt"; then
+	incompatible_opts=`echo "$git_am_opt" | sed -e 's/ -q//'`
+	if test -n "$interactive_rebase"
+	then
+		if test -n "$incompatible_opts"
+		then
+			die "$(gettext "error: cannot combine interactive options (--interactive, --exec, --rebase-merges, --preserve-merges, --keep-empty, --root + --onto) with am options ($incompatible_opts)")"
+		fi
+	fi
+	if test -n "$do_merge"; then
+		if test -n "$incompatible_opts"
+		then
+			die "$(gettext "error: cannot combine merge options (--merge, --strategy, --strategy-option) with am options ($incompatible_opts)")"
+		fi
+	fi
+fi
+
 if test -n "$signoff"
 then
 	test -n "$preserve_merges" &&

index 04cdae921b..66a83363bf 100755
@@ -34,27 +34,27 @@ test_expect_success 'setup' '
 test_run_rebase () {
 	opt=$1
 	shift
-	test_expect_failure "$opt incompatible with --merge" "
+	test_expect_success "$opt incompatible with --merge" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --merge A
 	"
 
-	test_expect_failure "$opt incompatible with --strategy=ours" "
+	test_expect_success "$opt incompatible with --strategy=ours" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --strategy=ours A
 	"
 
-	test_expect_failure "$opt incompatible with --strategy-option=ours" "
+	test_expect_success "$opt incompatible with --strategy-option=ours" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --strategy=ours A
 	"
 
-	test_expect_failure "$opt incompatible with --interactive" "
+	test_expect_success "$opt incompatible with --interactive" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --interactive A
 	"
 
-	test_expect_failure "$opt incompatible with --exec" "
+	test_expect_success "$opt incompatible with --exec" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --exec 'true' A
 	"

index 0e20a66e73..adccc15284 100644
@@ -243,11 +243,15 @@ leave out at most one of A and B, in which case it defaults to HEAD.
 --keep-empty::
 	Keep the commits that do not change anything from its
 	parents in the result.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --allow-empty-message::
 	By default, rebasing commits with an empty message will fail.
 	This option overrides that behavior, allowing commits with empty
 	messages to be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --skip::
 	Restart the rebasing process by skipping the current patch.

@@ -271,6 +275,8 @@ branch on top of the <upstream> branch.  Because of this, when a merge
 conflict happens, the side reported as 'ours' is the so-far rebased
 series, starting with <upstream>, and 'theirs' is the working branch.  In
 other words, the sides are swapped.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -s <strategy>::
 --strategy=<strategy>::

@@ -280,8 +286,10 @@ other words, the sides are swapped.
 +
 Because 'git rebase' replays each commit from the working branch
 on top of the <upstream> branch using the given strategy, using
-the 'ours' strategy simply discards all patches from the <branch>,
+the 'ours' strategy simply empties all patches from the <branch>,
 which makes little sense.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -X <strategy-option>::
 --strategy-option=<strategy-option>::

@@ -289,6 +297,8 @@ which makes little sense.
 	This implies `--merge` and, if no strategy has been
 	specified, `-s recursive`.  Note the reversal of 'ours' and
 	'theirs' as noted above for the `-m` option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -S[<keyid>]::
 --gpg-sign[=<keyid>]::

@@ -324,6 +334,8 @@ which makes little sense.
 	and after each change.  When fewer lines of surrounding
 	context exist they all must match.  By default no context is
 	ever ignored.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -f::
 --force-rebase::

@@ -355,19 +367,22 @@ default is `--no-fork-point`, otherwise the default is `--fork-point`.
 --whitespace=<option>::
 	These flag are passed to the 'git apply' program
 	(see linkgit:git-apply[1]) that applies the patch.
-	Incompatible with the --interactive option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --committer-date-is-author-date::
 --ignore-date::
 	These flags are passed to 'git am' to easily change the dates
 	of the rebased commits (see linkgit:git-am[1]).
-	Incompatible with the --interactive option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --signoff::
 	Add a Signed-off-by: trailer to all the rebased commits. Note
 	that if `--interactive` is given then only commits marked to be
-	picked, edited or reworded will have the trailer added. Incompatible
-	with the `--preserve-merges` option.
+	picked, edited or reworded will have the trailer added.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -i::
 --interactive::

@@ -378,6 +393,8 @@ default is `--no-fork-point`, otherwise the default is `--fork-point`.
 The commit list format can be changed by setting the configuration option
 rebase.instructionFormat.  A customized instruction format will automatically
 have the long commit hash prepended to the format.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -r::
 --rebase-merges[=(rebase-cousins|no-rebase-cousins)]::

@@ -404,7 +421,7 @@ It is currently only possible to recreate the merge commits using the
 `recursive` merge strategy; Different merge strategies can be used only via
 explicit `exec git merge -s <strategy> [...]` commands.
 +
-See also REBASING MERGES below.
+See also REBASING MERGES and INCOMPATIBLE OPTIONS below.
 
 -p::
 --preserve-merges::

@@ -415,6 +432,8 @@ See also REBASING MERGES below.
 This uses the `--interactive` machinery internally, but combining it
 with the `--interactive` option explicitly is generally not a good
 idea unless you know what you are doing (see BUGS below).
++
+See also INCOMPATIBLE OPTIONS below.
 
 -x <cmd>::
 --exec <cmd>::

@@ -437,6 +456,8 @@ squash/fixup series.
 +
 This uses the `--interactive` machinery internally, but it can be run
 without an explicit `--interactive`.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --root::
 	Rebase all commits reachable from <branch>, instead of

@@ -447,6 +468,8 @@ without an explicit `--interactive`.
 	When used together with both --onto and --preserve-merges,
 	'all' root commits will be rewritten to have <newbase> as parent
 	instead.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --autosquash::
 --no-autosquash::

@@ -461,11 +484,11 @@ without an explicit `--interactive`.
 	too.  The recommended way to create fixup/squash commits is by using
 	the `--fixup`/`--squash` options of linkgit:git-commit[1].
 +
-This option is only valid when the `--interactive` option is used.
-+
 If the `--autosquash` option is enabled by default using the
 configuration variable `rebase.autoSquash`, this option can be
 used to override and disable this setting.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --autostash::
 --no-autostash::

@@ -487,6 +510,51 @@ recreates the topic branch with fresh commits so it can be remerged
 successfully without needing to "revert the reversion" (see the
 link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
 
+INCOMPATIBLE OPTIONS
+--------------------
+
+git-rebase has many flags that are incompatible with each other,
+predominantly due to the fact that it has three different underlying
+implementations:
+
+ * one based on linkgit:git-am[1] (the default)
+ * one based on linkgit:git-merge-recursive[1] (merge backend)
+ * one based on linkgit:git-cherry-pick[1] (interactive backend)
+
+Flags only understood by the am backend:
+
+ * --committer-date-is-author-date
+ * --ignore-date
+ * --whitespace
+ * --ignore-whitespace
+ * -C
+
+Flags understood by both merge and interactive backends:
+
+ * --merge
+ * --strategy
+ * --strategy-option
+ * --allow-empty-message
+
+Flags only understood by the interactive backend:
+
+ * --[no-]autosquash
+ * --rebase-merges
+ * --preserve-merges
+ * --interactive
+ * --exec
+ * --keep-empty
+ * --autosquash
+ * --edit-todo
+ * --root + --onto
+
+Other incompatible flag pairs:
+
+ * --preserve-merges && --interactive
+ * --preserve-merges && --signoff
+ * --preserve-merges && --rebase-merges
+ * --rebase-merges && --strategy
+
 include::merge-strategies.txt[]
 
 NOTES

index 40be59ecc4..bf71b7fa20 100755
@@ -20,23 +20,23 @@ onto=!             rebase onto given branch instead of upstream
 r,rebase-merges?   try to rebase merges instead of skipping them
 p,preserve-merges! try to recreate merges instead of ignoring them
 s,strategy=!       use the given merge strategy
+X,strategy-option=! pass the argument through to the merge strategy
 no-ff!             cherry-pick all commits, even if unchanged
+f,force-rebase!    cherry-pick all commits, even if unchanged
 m,merge!           use merging strategies to rebase
 i,interactive!     let the user edit the list of commits to rebase
 x,exec=!           add exec lines after each commit of the editable list
 k,keep-empty	   preserve empty commits during rebase
 allow-empty-message allow rebasing commits with empty messages
-f,force-rebase!    force rebase even if branch is up to date
-X,strategy-option=! pass the argument through to the merge strategy
 stat!              display a diffstat of what changed upstream
 n,no-stat!         do not show diffstat of what changed upstream
 verify             allow pre-rebase hook to run
 rerere-autoupdate  allow rerere to update index with resolved conflicts
 root!              rebase all reachable commits up to the root(s)
 autosquash         move commits that begin with squash!/fixup! under -i
+signoff            add a Signed-off-by: line to each commit
 committer-date-is-author-date! passed to 'git am'
 ignore-date!       passed to 'git am'
-signoff            passed to 'git am'
 whitespace=!       passed to 'git apply'
 ignore-whitespace! passed to 'git apply'
 C=!                passed to 'git apply'

new file mode 100755
index 0000000000..04cdae921b
@@ -0,0 +1,69 @@
+#!/bin/sh
+
+test_description='test if rebase detects and aborts on incompatible options'
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_seq 2 9 >foo &&
+	git add foo &&
+	git commit -m orig &&
+
+	git branch A &&
+	git branch B &&
+
+	git checkout A &&
+	test_seq 1 9 >foo &&
+	git add foo &&
+	git commit -m A &&
+
+	git checkout B &&
+	# This is indented with HT SP HT.
+	echo "	 	foo();" >>foo &&
+	git add foo &&
+	git commit -m B
+'
+
+#
+# Rebase has lots of useful options like --whitepsace=fix, which are
+# actually all built in terms of flags to git-am.  Since neither
+# --merge nor --interactive (nor any options that imply those two) use
+# git-am, using them together will result in flags like --whitespace=fix
+# being ignored.  Make sure rebase warns the user and aborts instead.
+#
+
+test_run_rebase () {
+	opt=$1
+	shift
+	test_expect_failure "$opt incompatible with --merge" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --merge A
+	"
+
+	test_expect_failure "$opt incompatible with --strategy=ours" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --strategy=ours A
+	"
+
+	test_expect_failure "$opt incompatible with --strategy-option=ours" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --strategy=ours A
+	"
+
+	test_expect_failure "$opt incompatible with --interactive" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --interactive A
+	"
+
+	test_expect_failure "$opt incompatible with --exec" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --exec 'true' A
+	"
+
+}
+
+test_run_rebase --whitespace=fix
+test_run_rebase --ignore-whitespace
+test_run_rebase --committer-date-is-author-date
+test_run_rebase -C4
+
+test_done

index bf71b7fa20..5f891214fa 100755
@@ -503,6 +503,23 @@ then
 	git_format_patch_opt="$git_format_patch_opt --progress"
 fi
 
+if test -n "$git_am_opt"; then
+	incompatible_opts=$(echo "$git_am_opt" | sed -e 's/ -q//')
+	if test -n "$interactive_rebase"
+	then
+		if test -n "$incompatible_opts"
+		then
+			die "$(gettext "error: cannot combine interactive options (--interactive, --exec, --rebase-merges, --preserve-merges, --keep-empty, --root + --onto) with am options ($incompatible_opts)")"
+		fi
+	fi
+	if test -n "$do_merge"; then
+		if test -n "$incompatible_opts"
+		then
+			die "$(gettext "error: cannot combine merge options (--merge, --strategy, --strategy-option) with am options ($incompatible_opts)")"
+		fi
+	fi
+fi
+
 if test -n "$signoff"
 then
 	test -n "$preserve_merges" &&

index 04cdae921b..66a83363bf 100755
@@ -34,27 +34,27 @@ test_expect_success 'setup' '
 test_run_rebase () {
 	opt=$1
 	shift
-	test_expect_failure "$opt incompatible with --merge" "
+	test_expect_success "$opt incompatible with --merge" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --merge A
 	"
 
-	test_expect_failure "$opt incompatible with --strategy=ours" "
+	test_expect_success "$opt incompatible with --strategy=ours" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --strategy=ours A
 	"
 
-	test_expect_failure "$opt incompatible with --strategy-option=ours" "
+	test_expect_success "$opt incompatible with --strategy-option=ours" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --strategy=ours A
 	"
 
-	test_expect_failure "$opt incompatible with --interactive" "
+	test_expect_success "$opt incompatible with --interactive" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --interactive A
 	"
 
-	test_expect_failure "$opt incompatible with --exec" "
+	test_expect_success "$opt incompatible with --exec" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --exec 'true' A
 	"

index adccc15284..0dbfab06d0 100644
@@ -555,6 +555,63 @@ Other incompatible flag pairs:
  * --preserve-merges && --rebase-merges
  * --rebase-merges && --strategy
 
+BEHAVIORAL INCONSISTENCIES
+--------------------------
+
+  * --no-ff vs. --force-rebase
+
+    These options are actually identical, though their description
+    leads people to believe they might not be.
+
+ * empty commits:
+
+    am-based rebase will drop any "empty" commits, whether the
+    commit started empty (had no changes relative to its parent to
+    start with) or ended empty (all changes were already applied
+    upstream in other commits).
+
+    merge-based rebase does the same.
+
+    interactive-based rebase will by default drop commits that
+    started empty and halt if it hits a commit that ended up empty.
+    The --keep-empty option exists for interactive rebases to allow
+    it to keep commits that started empty.
+
+  * empty commit messages:
+
+    am-based rebase will silently apply commits with empty commit
+    messages.
+
+    merge-based and interactive-based rebases will by default halt
+    on any such commits.  The --allow-empty-message option exists to
+    allow interactive-based rebases to apply such commits without
+    halting.
+
+  * directory rename detection:
+
+    merge-based and interactive-based rebases work fine with
+    directory rename detection.  am-based rebases sometimes do not.
+
+    git-am tries to avoid a full three way merge, instead calling
+    git-apply.  That prevents us from detecting renames at all,
+    which may defeat the directory rename detection.  There is a
+    fallback, though; if the initial git-apply fails and the user
+    has specified the -3 option, git-am will fall back to a three
+    way merge.  However, git-am lacks the necessary information to
+    do a "real" three way merge.  Instead, it has to use
+    build_fake_ancestor() to get a merge base that is missing files
+    whose rename may have been important to detect for directory
+    rename detection to function.
+
+    Since am-based rebases work by first generating a bunch of
+    patches (which no longer record what the original commits were
+    and thus don't have the necessary info from which we can find a
+    real merge-base), and then calling git-am, this implies that
+    am-based rebases will not always successfully detect directory
+    renames either.  merged-based rebases (rebase -m) and
+    cherry-pick-based rebases (rebase -i) are not affected by this
+    shortcoming.
+
 include::merge-strategies.txt[]
 
 NOTES

index 0dbfab06d0..7a2ed9efdc 100644
@@ -337,16 +337,18 @@ See also INCOMPATIBLE OPTIONS below.
 +
 See also INCOMPATIBLE OPTIONS below.
 
--f::
+--no-ff::
 --force-rebase::
-	Force a rebase even if the current branch is up to date and
-	the command without `--force` would return without doing anything.
+-f::
+	Individually replay all rebased commits instead of fast-forwarding
+	over the unchanged ones.  This ensures that the entire history of
+	the rebased branch is composed of new commits.
 +
-You may find this (or --no-ff with an interactive rebase) helpful after
-reverting a topic branch merge, as this option recreates the topic branch with
-fresh commits so it can be remerged successfully without needing to "revert
-the reversion" (see the
-link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
+You may find this helpful after reverting a topic branch merge, as this option
+recreates the topic branch with fresh commits so it can be remerged
+successfully without needing to "revert the reversion" (see the
+link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for
+details).
 
 --fork-point::
 --no-fork-point::

@@ -498,18 +500,6 @@ See also INCOMPATIBLE OPTIONS below.
 	with care: the final stash application after a successful
 	rebase might result in non-trivial conflicts.
 
---no-ff::
-	With --interactive, cherry-pick all rebased commits instead of
-	fast-forwarding over the unchanged ones.  This ensures that the
-	entire history of the rebased branch is composed of new commits.
-+
-Without --interactive, this is a synonym for --force-rebase.
-+
-You may find this helpful after reverting a topic branch merge, as this option
-recreates the topic branch with fresh commits so it can be remerged
-successfully without needing to "revert the reversion" (see the
-link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
-
 INCOMPATIBLE OPTIONS
 --------------------
 

@@ -558,11 +548,6 @@ Other incompatible flag pairs:
 BEHAVIORAL INCONSISTENCIES
 --------------------------
 
-  * --no-ff vs. --force-rebase
-
-    These options are actually identical, though their description
-    leads people to believe they might not be.
-
  * empty commits:
 
     am-based rebase will drop any "empty" commits, whether the

index 7a2ed9efdc..a5608f481f 100644
@@ -562,16 +562,6 @@ BEHAVIORAL INCONSISTENCIES
     The --keep-empty option exists for interactive rebases to allow
     it to keep commits that started empty.
 
-  * empty commit messages:
-
-    am-based rebase will silently apply commits with empty commit
-    messages.
-
-    merge-based and interactive-based rebases will by default halt
-    on any such commits.  The --allow-empty-message option exists to
-    allow interactive-based rebases to apply such commits without
-    halting.
-
   * directory rename detection:
 
     merge-based and interactive-based rebases work fine with

index 5f891214fa..bf033da4e5 100755
@@ -95,7 +95,7 @@ rebase_cousins=
 preserve_merges=
 autosquash=
 keep_empty=
-allow_empty_message=
+allow_empty_message=--allow-empty-message
 signoff=
 test "$(git config --bool rebase.autosquash)" = "true" && autosquash=t
 case "$(git config --bool commit.gpgsign)" in

index c65826ddac..f84fa63b15 100755
@@ -553,15 +553,16 @@ test_expect_success '--continue tries to commit, even for "edit"' '
 '
 
 test_expect_success 'aborted --continue does not squash commits after "edit"' '
+	test_when_finished "git rebase --abort" &&
 	old=$(git rev-parse HEAD) &&
 	test_tick &&
 	set_fake_editor &&
 	FAKE_LINES="edit 1" git rebase -i HEAD^ &&
 	echo "edited again" > file7 &&
 	git add file7 &&
-	test_must_fail env FAKE_COMMIT_MESSAGE=" " git rebase --continue &&
-	test $old = $(git rev-parse HEAD) &&
-	git rebase --abort
+	echo all the things >>conflict &&
+	test_must_fail git rebase --continue &&
+	test $old = $(git rev-parse HEAD)
 '
 
 test_expect_success 'auto-amend only edited commits after "edit"' '

index cb7c6de84a..da94dddc86 100755
@@ -77,19 +77,14 @@ test_expect_success 'rebase commit with diff in message' '
 '
 
 test_expect_success 'rebase -m commit with empty message' '
-	test_must_fail git rebase -m master empty-message-merge &&
-	git rebase --abort &&
-	git rebase -m --allow-empty-message master empty-message-merge
+	git rebase -m master empty-message-merge
 '
 
 test_expect_success 'rebase -i commit with empty message' '
 	git checkout diff-in-message &&
 	set_fake_editor &&
-	test_must_fail env FAKE_COMMIT_MESSAGE=" " FAKE_LINES="reword 1" \
-		git rebase -i HEAD^ &&
-	git rebase --abort &&
-	FAKE_COMMIT_MESSAGE=" " FAKE_LINES="reword 1" \
-		git rebase -i --allow-empty-message HEAD^
+	env FAKE_COMMIT_MESSAGE=" " FAKE_LINES="reword 1" \
+		git rebase -i HEAD^
 '
 
 test_done

index 0e20a66e73..7de6523931 100644
@@ -243,11 +243,15 @@ leave out at most one of A and B, in which case it defaults to HEAD.
 --keep-empty::
 	Keep the commits that do not change anything from its
 	parents in the result.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --allow-empty-message::
 	By default, rebasing commits with an empty message will fail.
 	This option overrides that behavior, allowing commits with empty
 	messages to be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --skip::
 	Restart the rebasing process by skipping the current patch.

@@ -271,6 +275,8 @@ branch on top of the <upstream> branch.  Because of this, when a merge
 conflict happens, the side reported as 'ours' is the so-far rebased
 series, starting with <upstream>, and 'theirs' is the working branch.  In
 other words, the sides are swapped.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -s <strategy>::
 --strategy=<strategy>::

@@ -280,8 +286,10 @@ other words, the sides are swapped.
 +
 Because 'git rebase' replays each commit from the working branch
 on top of the <upstream> branch using the given strategy, using
-the 'ours' strategy simply discards all patches from the <branch>,
+the 'ours' strategy simply empties all patches from the <branch>,
 which makes little sense.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -X <strategy-option>::
 --strategy-option=<strategy-option>::

@@ -289,6 +297,8 @@ which makes little sense.
 	This implies `--merge` and, if no strategy has been
 	specified, `-s recursive`.  Note the reversal of 'ours' and
 	'theirs' as noted above for the `-m` option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -S[<keyid>]::
 --gpg-sign[=<keyid>]::

@@ -324,6 +334,8 @@ which makes little sense.
 	and after each change.  When fewer lines of surrounding
 	context exist they all must match.  By default no context is
 	ever ignored.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -f::
 --force-rebase::

@@ -355,19 +367,22 @@ default is `--no-fork-point`, otherwise the default is `--fork-point`.
 --whitespace=<option>::
 	These flag are passed to the 'git apply' program
 	(see linkgit:git-apply[1]) that applies the patch.
-	Incompatible with the --interactive option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --committer-date-is-author-date::
 --ignore-date::
 	These flags are passed to 'git am' to easily change the dates
 	of the rebased commits (see linkgit:git-am[1]).
-	Incompatible with the --interactive option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --signoff::
 	Add a Signed-off-by: trailer to all the rebased commits. Note
 	that if `--interactive` is given then only commits marked to be
-	picked, edited or reworded will have the trailer added. Incompatible
-	with the `--preserve-merges` option.
+	picked, edited or reworded will have the trailer added.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -i::
 --interactive::

@@ -378,6 +393,8 @@ default is `--no-fork-point`, otherwise the default is `--fork-point`.
 The commit list format can be changed by setting the configuration option
 rebase.instructionFormat.  A customized instruction format will automatically
 have the long commit hash prepended to the format.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -r::
 --rebase-merges[=(rebase-cousins|no-rebase-cousins)]::

@@ -404,7 +421,7 @@ It is currently only possible to recreate the merge commits using the
 `recursive` merge strategy; Different merge strategies can be used only via
 explicit `exec git merge -s <strategy> [...]` commands.
 +
-See also REBASING MERGES below.
+See also REBASING MERGES and INCOMPATIBLE OPTIONS below.
 
 -p::
 --preserve-merges::

@@ -415,6 +432,8 @@ See also REBASING MERGES below.
 This uses the `--interactive` machinery internally, but combining it
 with the `--interactive` option explicitly is generally not a good
 idea unless you know what you are doing (see BUGS below).
++
+See also INCOMPATIBLE OPTIONS below.
 
 -x <cmd>::
 --exec <cmd>::

@@ -437,6 +456,8 @@ squash/fixup series.
 +
 This uses the `--interactive` machinery internally, but it can be run
 without an explicit `--interactive`.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --root::
 	Rebase all commits reachable from <branch>, instead of

@@ -447,6 +468,8 @@ without an explicit `--interactive`.
 	When used together with both --onto and --preserve-merges,
 	'all' root commits will be rewritten to have <newbase> as parent
 	instead.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --autosquash::
 --no-autosquash::

@@ -461,11 +484,11 @@ without an explicit `--interactive`.
 	too.  The recommended way to create fixup/squash commits is by using
 	the `--fixup`/`--squash` options of linkgit:git-commit[1].
 +
-This option is only valid when the `--interactive` option is used.
-+
 If the `--autosquash` option is enabled by default using the
 configuration variable `rebase.autoSquash`, this option can be
 used to override and disable this setting.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --autostash::
 --no-autostash::

@@ -487,6 +510,52 @@ recreates the topic branch with fresh commits so it can be remerged
 successfully without needing to "revert the reversion" (see the
 link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
 
+INCOMPATIBLE OPTIONS
+--------------------
+
+git-rebase has many flags that are incompatible with each other,
+predominantly due to the fact that it has three different underlying
+implementations:
+
+ * one based on linkgit:git-am[1] (the default)
+ * one based on linkgit:git-merge-recursive[1] (merge backend)
+ * one based on linkgit:git-cherry-pick[1] (interactive backend)
+
+Flags only understood by the am backend:
+
+ * --committer-date-is-author-date
+ * --ignore-date
+ * --whitespace
+ * --ignore-whitespace
+ * -C
+
+Flags understood by both merge and interactive backends:
+
+ * --merge
+ * --strategy
+ * --strategy-option
+ * --allow-empty-message
+
+Flags only understood by the interactive backend:
+
+ * --[no-]autosquash
+ * --rebase-merges
+ * --preserve-merges
+ * --interactive
+ * --exec
+ * --keep-empty
+ * --autosquash
+ * --edit-todo
+ * --root when used in combination with --onto
+
+Other incompatible flag pairs:
+
+ * --preserve-merges and --interactive
+ * --preserve-merges and --signoff
+ * --preserve-merges and --rebase-merges
+ * --rebase-merges and --strategy
+ * --rebase-merges and --strategy-option
+
 include::merge-strategies.txt[]
 
 NOTES

index 40be59ecc4..bf71b7fa20 100755
@@ -20,23 +20,23 @@ onto=!             rebase onto given branch instead of upstream
 r,rebase-merges?   try to rebase merges instead of skipping them
 p,preserve-merges! try to recreate merges instead of ignoring them
 s,strategy=!       use the given merge strategy
+X,strategy-option=! pass the argument through to the merge strategy
 no-ff!             cherry-pick all commits, even if unchanged
+f,force-rebase!    cherry-pick all commits, even if unchanged
 m,merge!           use merging strategies to rebase
 i,interactive!     let the user edit the list of commits to rebase
 x,exec=!           add exec lines after each commit of the editable list
 k,keep-empty	   preserve empty commits during rebase
 allow-empty-message allow rebasing commits with empty messages
-f,force-rebase!    force rebase even if branch is up to date
-X,strategy-option=! pass the argument through to the merge strategy
 stat!              display a diffstat of what changed upstream
 n,no-stat!         do not show diffstat of what changed upstream
 verify             allow pre-rebase hook to run
 rerere-autoupdate  allow rerere to update index with resolved conflicts
 root!              rebase all reachable commits up to the root(s)
 autosquash         move commits that begin with squash!/fixup! under -i
+signoff            add a Signed-off-by: line to each commit
 committer-date-is-author-date! passed to 'git am'
 ignore-date!       passed to 'git am'
-signoff            passed to 'git am'
 whitespace=!       passed to 'git apply'
 ignore-whitespace! passed to 'git apply'
 C=!                passed to 'git apply'

new file mode 100755
index 0000000000..157374143f
@@ -0,0 +1,89 @@
+#!/bin/sh
+
+test_description='test if rebase detects and aborts on incompatible options'
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_seq 2 9 >foo &&
+	git add foo &&
+	git commit -m orig &&
+
+	git branch A &&
+	git branch B &&
+
+	git checkout A &&
+	test_seq 1 9 >foo &&
+	git add foo &&
+	git commit -m A &&
+
+	git checkout B &&
+	# This is indented with HT SP HT.
+	echo "	 	foo();" >>foo &&
+	git add foo &&
+	git commit -m B
+'
+
+#
+# Rebase has lots of useful options like --whitepsace=fix, which are
+# actually all built in terms of flags to git-am.  Since neither
+# --merge nor --interactive (nor any options that imply those two) use
+# git-am, using them together will result in flags like --whitespace=fix
+# being ignored.  Make sure rebase warns the user and aborts instead.
+#
+
+test_run_rebase () {
+	opt=$1
+	shift
+	test_expect_failure "$opt incompatible with --merge" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --merge A
+	"
+
+	test_expect_failure "$opt incompatible with --strategy=ours" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --strategy=ours A
+	"
+
+	test_expect_failure "$opt incompatible with --strategy-option=ours" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --strategy=ours A
+	"
+
+	test_expect_failure "$opt incompatible with --interactive" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --interactive A
+	"
+
+	test_expect_failure "$opt incompatible with --exec" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --exec 'true' A
+	"
+
+}
+
+test_run_rebase --whitespace=fix
+test_run_rebase --ignore-whitespace
+test_run_rebase --committer-date-is-author-date
+test_run_rebase -C4
+
+test_expect_success '--preserve-merges incompatible with --signoff' '
+	git checkout B^0 &&
+	test_must_fail git rebase --preserve-merges --signoff A
+'
+
+test_expect_failure '--preserve-merges incompatible with --rebase-merges' '
+	git checkout B^0 &&
+	test_must_fail git rebase --preserve-merges --rebase-merges A
+'
+
+test_expect_failure '--rebase-merges incompatible with --strategy' '
+	git checkout B^0 &&
+	test_must_fail git rebase --rebase-merges -s resolve A
+'
+
+test_expect_failure '--rebase-merges incompatible with --strategy-option' '
+	git checkout B^0 &&
+	test_must_fail git rebase --rebase-merges -Xignore-space-change A
+'
+
+test_done

index bf71b7fa20..590bdbb12a 100755
@@ -503,6 +503,23 @@ then
 	git_format_patch_opt="$git_format_patch_opt --progress"
 fi
 
+if test -n "$git_am_opt"; then
+	incompatible_opts=$(echo "$git_am_opt" | sed -e 's/ -q//')
+	if test -n "$interactive_rebase"
+	then
+		if test -n "$incompatible_opts"
+		then
+			die "$(gettext "error: cannot combine interactive options (--interactive, --exec, --rebase-merges, --preserve-merges, --keep-empty, --root + --onto) with am options ($incompatible_opts)")"
+		fi
+	fi
+	if test -n "$do_merge"; then
+		if test -n "$incompatible_opts"
+		then
+			die "$(gettext "error: cannot combine merge options (--merge, --strategy, --strategy-option) with am options ($incompatible_opts)")"
+		fi
+	fi
+fi
+
 if test -n "$signoff"
 then
 	test -n "$preserve_merges" &&

@@ -511,6 +528,23 @@ then
 	force_rebase=t
 fi
 
+if test -n "$preserve_merges"
+then
+	# Note: incompatibility with --signoff handled in signoff block above
+	# Note: incompatibility with --interactive is just a strong warning;
+	#       git-rebase.txt caveats with "unless you know what you are doing"
+	test -n "$rebase_merges" &&
+		die "$(gettext "error: cannot combine '--preserve_merges' with '--rebase-merges'")"
+fi
+
+if test -n "$rebase_merges"
+then
+	test -n "$strategy_opts" &&
+		die "$(gettext "error: cannot combine '--rebase_merges' with '--strategy-option'")"
+	test -n "$strategy" &&
+		die "$(gettext "error: cannot combine '--rebase_merges' with '--strategy'")"
+fi
+
 if test -z "$rebase_root"
 then
 	case "$#" in

index 157374143f..415d5226bf 100755
@@ -34,27 +34,27 @@ test_expect_success 'setup' '
 test_run_rebase () {
 	opt=$1
 	shift
-	test_expect_failure "$opt incompatible with --merge" "
+	test_expect_success "$opt incompatible with --merge" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --merge A
 	"
 
-	test_expect_failure "$opt incompatible with --strategy=ours" "
+	test_expect_success "$opt incompatible with --strategy=ours" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --strategy=ours A
 	"
 
-	test_expect_failure "$opt incompatible with --strategy-option=ours" "
+	test_expect_success "$opt incompatible with --strategy-option=ours" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --strategy=ours A
 	"
 
-	test_expect_failure "$opt incompatible with --interactive" "
+	test_expect_success "$opt incompatible with --interactive" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --interactive A
 	"
 
-	test_expect_failure "$opt incompatible with --exec" "
+	test_expect_success "$opt incompatible with --exec" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --exec 'true' A
 	"

@@ -71,17 +71,17 @@ test_expect_success '--preserve-merges incompatible with --signoff' '
 	test_must_fail git rebase --preserve-merges --signoff A
 '
 
-test_expect_failure '--preserve-merges incompatible with --rebase-merges' '
+test_expect_success '--preserve-merges incompatible with --rebase-merges' '
 	git checkout B^0 &&
 	test_must_fail git rebase --preserve-merges --rebase-merges A
 '
 
-test_expect_failure '--rebase-merges incompatible with --strategy' '
+test_expect_success '--rebase-merges incompatible with --strategy' '
 	git checkout B^0 &&
 	test_must_fail git rebase --rebase-merges -s resolve A
 '
 
-test_expect_failure '--rebase-merges incompatible with --strategy-option' '
+test_expect_success '--rebase-merges incompatible with --strategy-option' '
 	git checkout B^0 &&
 	test_must_fail git rebase --rebase-merges -Xignore-space-change A
 '

index 7de6523931..340137e2cf 100644
@@ -556,6 +556,63 @@ Other incompatible flag pairs:
  * --rebase-merges and --strategy
  * --rebase-merges and --strategy-option
 
+BEHAVIORAL INCONSISTENCIES
+--------------------------
+
+  * --no-ff vs. --force-rebase
+
+    These options are actually identical, though their description
+    leads people to believe they might not be.
+
+ * empty commits:
+
+    am-based rebase will drop any "empty" commits, whether the
+    commit started empty (had no changes relative to its parent to
+    start with) or ended empty (all changes were already applied
+    upstream in other commits).
+
+    merge-based rebase does the same.
+
+    interactive-based rebase will by default drop commits that
+    started empty and halt if it hits a commit that ended up empty.
+    The --keep-empty option exists for interactive rebases to allow
+    it to keep commits that started empty.
+
+  * empty commit messages:
+
+    am-based rebase will silently apply commits with empty commit
+    messages.
+
+    merge-based and interactive-based rebases will by default halt
+    on any such commits.  The --allow-empty-message option exists to
+    allow interactive-based rebases to apply such commits without
+    halting.
+
+  * directory rename detection:
+
+    merge-based and interactive-based rebases work fine with
+    directory rename detection.  am-based rebases sometimes do not.
+
+    git-am tries to avoid a full three way merge, instead calling
+    git-apply.  That prevents us from detecting renames at all,
+    which may defeat the directory rename detection.  There is a
+    fallback, though; if the initial git-apply fails and the user
+    has specified the -3 option, git-am will fall back to a three
+    way merge.  However, git-am lacks the necessary information to
+    do a "real" three way merge.  Instead, it has to use
+    build_fake_ancestor() to get a merge base that is missing files
+    whose rename may have been important to detect for directory
+    rename detection to function.
+
+    Since am-based rebases work by first generating a bunch of
+    patches (which no longer record what the original commits were
+    and thus don't have the necessary info from which we can find a
+    real merge-base), and then calling git-am, this implies that
+    am-based rebases will not always successfully detect directory
+    renames either.  merged-based rebases (rebase -m) and
+    cherry-pick-based rebases (rebase -i) are not affected by this
+    shortcoming.
+
 include::merge-strategies.txt[]
 
 NOTES

index 340137e2cf..1f422cd0a7 100644
@@ -337,16 +337,18 @@ See also INCOMPATIBLE OPTIONS below.
 +
 See also INCOMPATIBLE OPTIONS below.
 
--f::
+--no-ff::
 --force-rebase::
-	Force a rebase even if the current branch is up to date and
-	the command without `--force` would return without doing anything.
+-f::
+	Individually replay all rebased commits instead of fast-forwarding
+	over the unchanged ones.  This ensures that the entire history of
+	the rebased branch is composed of new commits.
 +
-You may find this (or --no-ff with an interactive rebase) helpful after
-reverting a topic branch merge, as this option recreates the topic branch with
-fresh commits so it can be remerged successfully without needing to "revert
-the reversion" (see the
-link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
+You may find this helpful after reverting a topic branch merge, as this option
+recreates the topic branch with fresh commits so it can be remerged
+successfully without needing to "revert the reversion" (see the
+link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for
+details).
 
 --fork-point::
 --no-fork-point::

@@ -498,18 +500,6 @@ See also INCOMPATIBLE OPTIONS below.
 	with care: the final stash application after a successful
 	rebase might result in non-trivial conflicts.
 
---no-ff::
-	With --interactive, cherry-pick all rebased commits instead of
-	fast-forwarding over the unchanged ones.  This ensures that the
-	entire history of the rebased branch is composed of new commits.
-+
-Without --interactive, this is a synonym for --force-rebase.
-+
-You may find this helpful after reverting a topic branch merge, as this option
-recreates the topic branch with fresh commits so it can be remerged
-successfully without needing to "revert the reversion" (see the
-link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
-
 INCOMPATIBLE OPTIONS
 --------------------
 

@@ -559,11 +549,6 @@ Other incompatible flag pairs:
 BEHAVIORAL INCONSISTENCIES
 --------------------------
 
-  * --no-ff vs. --force-rebase
-
-    These options are actually identical, though their description
-    leads people to believe they might not be.
-
  * empty commits:
 
     am-based rebase will drop any "empty" commits, whether the

index 1f422cd0a7..3addcf8218 100644
@@ -563,16 +563,6 @@ BEHAVIORAL INCONSISTENCIES
     The --keep-empty option exists for interactive rebases to allow
     it to keep commits that started empty.
 
-  * empty commit messages:
-
-    am-based rebase will silently apply commits with empty commit
-    messages.
-
-    merge-based and interactive-based rebases will by default halt
-    on any such commits.  The --allow-empty-message option exists to
-    allow interactive-based rebases to apply such commits without
-    halting.
-
   * directory rename detection:
 
     merge-based and interactive-based rebases work fine with

index 590bdbb12a..a909a2cfb1 100755
@@ -95,7 +95,7 @@ rebase_cousins=
 preserve_merges=
 autosquash=
 keep_empty=
-allow_empty_message=
+allow_empty_message=--allow-empty-message
 signoff=
 test "$(git config --bool rebase.autosquash)" = "true" && autosquash=t
 case "$(git config --bool commit.gpgsign)" in

index 352a52e59d..81ce9fe7f9 100755
@@ -553,15 +553,16 @@ test_expect_success '--continue tries to commit, even for "edit"' '
 '
 
 test_expect_success 'aborted --continue does not squash commits after "edit"' '
+	test_when_finished "git rebase --abort" &&
 	old=$(git rev-parse HEAD) &&
 	test_tick &&
 	set_fake_editor &&
 	FAKE_LINES="edit 1" git rebase -i HEAD^ &&
 	echo "edited again" > file7 &&
 	git add file7 &&
-	test_must_fail env FAKE_COMMIT_MESSAGE=" " git rebase --continue &&
-	test $old = $(git rev-parse HEAD) &&
-	git rebase --abort
+	echo all the things >>conflict &&
+	test_must_fail git rebase --continue &&
+	test $old = $(git rev-parse HEAD)
 '
 
 test_expect_success 'auto-amend only edited commits after "edit"' '

index cb7c6de84a..da94dddc86 100755
@@ -77,19 +77,14 @@ test_expect_success 'rebase commit with diff in message' '
 '
 
 test_expect_success 'rebase -m commit with empty message' '
-	test_must_fail git rebase -m master empty-message-merge &&
-	git rebase --abort &&
-	git rebase -m --allow-empty-message master empty-message-merge
+	git rebase -m master empty-message-merge
 '
 
 test_expect_success 'rebase -i commit with empty message' '
 	git checkout diff-in-message &&
 	set_fake_editor &&
-	test_must_fail env FAKE_COMMIT_MESSAGE=" " FAKE_LINES="reword 1" \
-		git rebase -i HEAD^ &&
-	git rebase --abort &&
-	FAKE_COMMIT_MESSAGE=" " FAKE_LINES="reword 1" \
-		git rebase -i --allow-empty-message HEAD^
+	env FAKE_COMMIT_MESSAGE=" " FAKE_LINES="reword 1" \
+		git rebase -i HEAD^
 '
 
 test_done

index 0e20a66e73..b2d95e3fb9 100644
@@ -243,11 +243,15 @@ leave out at most one of A and B, in which case it defaults to HEAD.
 --keep-empty::
 	Keep the commits that do not change anything from its
 	parents in the result.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --allow-empty-message::
 	By default, rebasing commits with an empty message will fail.
 	This option overrides that behavior, allowing commits with empty
 	messages to be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --skip::
 	Restart the rebasing process by skipping the current patch.

@@ -271,6 +275,8 @@ branch on top of the <upstream> branch.  Because of this, when a merge
 conflict happens, the side reported as 'ours' is the so-far rebased
 series, starting with <upstream>, and 'theirs' is the working branch.  In
 other words, the sides are swapped.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -s <strategy>::
 --strategy=<strategy>::

@@ -280,8 +286,10 @@ other words, the sides are swapped.
 +
 Because 'git rebase' replays each commit from the working branch
 on top of the <upstream> branch using the given strategy, using
-the 'ours' strategy simply discards all patches from the <branch>,
+the 'ours' strategy simply empties all patches from the <branch>,
 which makes little sense.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -X <strategy-option>::
 --strategy-option=<strategy-option>::

@@ -289,6 +297,8 @@ which makes little sense.
 	This implies `--merge` and, if no strategy has been
 	specified, `-s recursive`.  Note the reversal of 'ours' and
 	'theirs' as noted above for the `-m` option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -S[<keyid>]::
 --gpg-sign[=<keyid>]::

@@ -324,6 +334,8 @@ which makes little sense.
 	and after each change.  When fewer lines of surrounding
 	context exist they all must match.  By default no context is
 	ever ignored.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -f::
 --force-rebase::

@@ -355,19 +367,22 @@ default is `--no-fork-point`, otherwise the default is `--fork-point`.
 --whitespace=<option>::
 	These flag are passed to the 'git apply' program
 	(see linkgit:git-apply[1]) that applies the patch.
-	Incompatible with the --interactive option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --committer-date-is-author-date::
 --ignore-date::
 	These flags are passed to 'git am' to easily change the dates
 	of the rebased commits (see linkgit:git-am[1]).
-	Incompatible with the --interactive option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --signoff::
 	Add a Signed-off-by: trailer to all the rebased commits. Note
 	that if `--interactive` is given then only commits marked to be
-	picked, edited or reworded will have the trailer added. Incompatible
-	with the `--preserve-merges` option.
+	picked, edited or reworded will have the trailer added.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -i::
 --interactive::

@@ -378,6 +393,8 @@ default is `--no-fork-point`, otherwise the default is `--fork-point`.
 The commit list format can be changed by setting the configuration option
 rebase.instructionFormat.  A customized instruction format will automatically
 have the long commit hash prepended to the format.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -r::
 --rebase-merges[=(rebase-cousins|no-rebase-cousins)]::

@@ -404,7 +421,7 @@ It is currently only possible to recreate the merge commits using the
 `recursive` merge strategy; Different merge strategies can be used only via
 explicit `exec git merge -s <strategy> [...]` commands.
 +
-See also REBASING MERGES below.
+See also REBASING MERGES and INCOMPATIBLE OPTIONS below.
 
 -p::
 --preserve-merges::

@@ -415,6 +432,8 @@ See also REBASING MERGES below.
 This uses the `--interactive` machinery internally, but combining it
 with the `--interactive` option explicitly is generally not a good
 idea unless you know what you are doing (see BUGS below).
++
+See also INCOMPATIBLE OPTIONS below.
 
 -x <cmd>::
 --exec <cmd>::

@@ -437,6 +456,8 @@ squash/fixup series.
 +
 This uses the `--interactive` machinery internally, but it can be run
 without an explicit `--interactive`.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --root::
 	Rebase all commits reachable from <branch>, instead of

@@ -447,6 +468,8 @@ without an explicit `--interactive`.
 	When used together with both --onto and --preserve-merges,
 	'all' root commits will be rewritten to have <newbase> as parent
 	instead.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --autosquash::
 --no-autosquash::

@@ -461,11 +484,11 @@ without an explicit `--interactive`.
 	too.  The recommended way to create fixup/squash commits is by using
 	the `--fixup`/`--squash` options of linkgit:git-commit[1].
 +
-This option is only valid when the `--interactive` option is used.
-+
 If the `--autosquash` option is enabled by default using the
 configuration variable `rebase.autoSquash`, this option can be
 used to override and disable this setting.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --autostash::
 --no-autostash::

@@ -487,6 +510,52 @@ recreates the topic branch with fresh commits so it can be remerged
 successfully without needing to "revert the reversion" (see the
 link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
 
+INCOMPATIBLE OPTIONS
+--------------------
+
+git-rebase has many flags that are incompatible with each other,
+predominantly due to the fact that it has three different underlying
+implementations:
+
+ * one based on linkgit:git-am[1] (the default)
+ * one based on git-merge-recursive (merge backend)
+ * one based on linkgit:git-cherry-pick[1] (interactive backend)
+
+Flags only understood by the am backend:
+
+ * --committer-date-is-author-date
+ * --ignore-date
+ * --whitespace
+ * --ignore-whitespace
+ * -C
+
+Flags understood by both merge and interactive backends:
+
+ * --merge
+ * --strategy
+ * --strategy-option
+ * --allow-empty-message
+
+Flags only understood by the interactive backend:
+
+ * --[no-]autosquash
+ * --rebase-merges
+ * --preserve-merges
+ * --interactive
+ * --exec
+ * --keep-empty
+ * --autosquash
+ * --edit-todo
+ * --root when used in combination with --onto
+
+Other incompatible flag pairs:
+
+ * --preserve-merges and --interactive
+ * --preserve-merges and --signoff
+ * --preserve-merges and --rebase-merges
+ * --rebase-merges and --strategy
+ * --rebase-merges and --strategy-option
+
 include::merge-strategies.txt[]
 
 NOTES

index 40be59ecc4..bf71b7fa20 100755
@@ -20,23 +20,23 @@ onto=!             rebase onto given branch instead of upstream
 r,rebase-merges?   try to rebase merges instead of skipping them
 p,preserve-merges! try to recreate merges instead of ignoring them
 s,strategy=!       use the given merge strategy
+X,strategy-option=! pass the argument through to the merge strategy
 no-ff!             cherry-pick all commits, even if unchanged
+f,force-rebase!    cherry-pick all commits, even if unchanged
 m,merge!           use merging strategies to rebase
 i,interactive!     let the user edit the list of commits to rebase
 x,exec=!           add exec lines after each commit of the editable list
 k,keep-empty	   preserve empty commits during rebase
 allow-empty-message allow rebasing commits with empty messages
-f,force-rebase!    force rebase even if branch is up to date
-X,strategy-option=! pass the argument through to the merge strategy
 stat!              display a diffstat of what changed upstream
 n,no-stat!         do not show diffstat of what changed upstream
 verify             allow pre-rebase hook to run
 rerere-autoupdate  allow rerere to update index with resolved conflicts
 root!              rebase all reachable commits up to the root(s)
 autosquash         move commits that begin with squash!/fixup! under -i
+signoff            add a Signed-off-by: line to each commit
 committer-date-is-author-date! passed to 'git am'
 ignore-date!       passed to 'git am'
-signoff            passed to 'git am'
 whitespace=!       passed to 'git apply'
 ignore-whitespace! passed to 'git apply'
 C=!                passed to 'git apply'

new file mode 100755
index 0000000000..2687a85254
@@ -0,0 +1,88 @@
+#!/bin/sh
+
+test_description='test if rebase detects and aborts on incompatible options'
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_seq 2 9 >foo &&
+	git add foo &&
+	git commit -m orig &&
+
+	git branch A &&
+	git branch B &&
+
+	git checkout A &&
+	test_seq 1 9 >foo &&
+	git add foo &&
+	git commit -m A &&
+
+	git checkout B &&
+	echo "q qfoo();" | q_to_tab >>foo &&
+	git add foo &&
+	git commit -m B
+'
+
+#
+# Rebase has lots of useful options like --whitepsace=fix, which are
+# actually all built in terms of flags to git-am.  Since neither
+# --merge nor --interactive (nor any options that imply those two) use
+# git-am, using them together will result in flags like --whitespace=fix
+# being ignored.  Make sure rebase warns the user and aborts instead.
+#
+
+test_rebase_am_only () {
+	opt=$1
+	shift
+	test_expect_failure "$opt incompatible with --merge" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --merge A
+	"
+
+	test_expect_failure "$opt incompatible with --strategy=ours" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --strategy=ours A
+	"
+
+	test_expect_failure "$opt incompatible with --strategy-option=ours" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --strategy=ours A
+	"
+
+	test_expect_failure "$opt incompatible with --interactive" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --interactive A
+	"
+
+	test_expect_failure "$opt incompatible with --exec" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --exec 'true' A
+	"
+
+}
+
+test_rebase_am_only --whitespace=fix
+test_rebase_am_only --ignore-whitespace
+test_rebase_am_only --committer-date-is-author-date
+test_rebase_am_only -C4
+
+test_expect_success '--preserve-merges incompatible with --signoff' '
+	git checkout B^0 &&
+	test_must_fail git rebase --preserve-merges --signoff A
+'
+
+test_expect_failure '--preserve-merges incompatible with --rebase-merges' '
+	git checkout B^0 &&
+	test_must_fail git rebase --preserve-merges --rebase-merges A
+'
+
+test_expect_failure '--rebase-merges incompatible with --strategy' '
+	git checkout B^0 &&
+	test_must_fail git rebase --rebase-merges -s resolve A
+'
+
+test_expect_failure '--rebase-merges incompatible with --strategy-option' '
+	git checkout B^0 &&
+	test_must_fail git rebase --rebase-merges -Xignore-space-change A
+'
+
+test_done

index bf71b7fa20..18ac8226c4 100755
@@ -503,6 +503,24 @@ then
 	git_format_patch_opt="$git_format_patch_opt --progress"
 fi
 
+if test -n "$git_am_opt"; then
+	incompatible_opts=$(echo " $git_am_opt " | \
+			    sed -e 's/ -q / /g' -e 's/^ \(.*\) $/\1/')
+	if test -n "$interactive_rebase"
+	then
+		if test -n "$incompatible_opts"
+		then
+			die "$(gettext "error: cannot combine interactive options (--interactive, --exec, --rebase-merges, --preserve-merges, --keep-empty, --root + --onto) with am options ($incompatible_opts)")"
+		fi
+	fi
+	if test -n "$do_merge"; then
+		if test -n "$incompatible_opts"
+		then
+			die "$(gettext "error: cannot combine merge options (--merge, --strategy, --strategy-option) with am options ($incompatible_opts)")"
+		fi
+	fi
+fi
+
 if test -n "$signoff"
 then
 	test -n "$preserve_merges" &&

@@ -511,6 +529,23 @@ then
 	force_rebase=t
 fi
 
+if test -n "$preserve_merges"
+then
+	# Note: incompatibility with --signoff handled in signoff block above
+	# Note: incompatibility with --interactive is just a strong warning;
+	#       git-rebase.txt caveats with "unless you know what you are doing"
+	test -n "$rebase_merges" &&
+		die "$(gettext "error: cannot combine '--preserve_merges' with '--rebase-merges'")"
+fi
+
+if test -n "$rebase_merges"
+then
+	test -n "$strategy_opts" &&
+		die "$(gettext "error: cannot combine '--rebase_merges' with '--strategy-option'")"
+	test -n "$strategy" &&
+		die "$(gettext "error: cannot combine '--rebase_merges' with '--strategy'")"
+fi
+
 if test -z "$rebase_root"
 then
 	case "$#" in

index 2687a85254..fc0ce150d1 100755
@@ -33,27 +33,27 @@ test_expect_success 'setup' '
 test_rebase_am_only () {
 	opt=$1
 	shift
-	test_expect_failure "$opt incompatible with --merge" "
+	test_expect_success "$opt incompatible with --merge" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --merge A
 	"
 
-	test_expect_failure "$opt incompatible with --strategy=ours" "
+	test_expect_success "$opt incompatible with --strategy=ours" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --strategy=ours A
 	"
 
-	test_expect_failure "$opt incompatible with --strategy-option=ours" "
+	test_expect_success "$opt incompatible with --strategy-option=ours" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --strategy=ours A
 	"
 
-	test_expect_failure "$opt incompatible with --interactive" "
+	test_expect_success "$opt incompatible with --interactive" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --interactive A
 	"
 
-	test_expect_failure "$opt incompatible with --exec" "
+	test_expect_success "$opt incompatible with --exec" "
 		git checkout B^0 &&
 		test_must_fail git rebase $opt --exec 'true' A
 	"

@@ -70,17 +70,17 @@ test_expect_success '--preserve-merges incompatible with --signoff' '
 	test_must_fail git rebase --preserve-merges --signoff A
 '
 
-test_expect_failure '--preserve-merges incompatible with --rebase-merges' '
+test_expect_success '--preserve-merges incompatible with --rebase-merges' '
 	git checkout B^0 &&
 	test_must_fail git rebase --preserve-merges --rebase-merges A
 '
 
-test_expect_failure '--rebase-merges incompatible with --strategy' '
+test_expect_success '--rebase-merges incompatible with --strategy' '
 	git checkout B^0 &&
 	test_must_fail git rebase --rebase-merges -s resolve A
 '
 
-test_expect_failure '--rebase-merges incompatible with --strategy-option' '
+test_expect_success '--rebase-merges incompatible with --strategy-option' '
 	git checkout B^0 &&
 	test_must_fail git rebase --rebase-merges -Xignore-space-change A
 '

index b2d95e3fb9..2f47495a4d 100644
@@ -337,16 +337,18 @@ See also INCOMPATIBLE OPTIONS below.
 +
 See also INCOMPATIBLE OPTIONS below.
 
--f::
+--no-ff::
 --force-rebase::
-	Force a rebase even if the current branch is up to date and
-	the command without `--force` would return without doing anything.
+-f::
+	Individually replay all rebased commits instead of fast-forwarding
+	over the unchanged ones.  This ensures that the entire history of
+	the rebased branch is composed of new commits.
 +
-You may find this (or --no-ff with an interactive rebase) helpful after
-reverting a topic branch merge, as this option recreates the topic branch with
-fresh commits so it can be remerged successfully without needing to "revert
-the reversion" (see the
-link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
+You may find this helpful after reverting a topic branch merge, as this option
+recreates the topic branch with fresh commits so it can be remerged
+successfully without needing to "revert the reversion" (see the
+link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for
+details).
 
 --fork-point::
 --no-fork-point::

@@ -498,18 +500,6 @@ See also INCOMPATIBLE OPTIONS below.
 	with care: the final stash application after a successful
 	rebase might result in non-trivial conflicts.
 
---no-ff::
-	With --interactive, cherry-pick all rebased commits instead of
-	fast-forwarding over the unchanged ones.  This ensures that the
-	entire history of the rebased branch is composed of new commits.
-+
-Without --interactive, this is a synonym for --force-rebase.
-+
-You may find this helpful after reverting a topic branch merge, as this option
-recreates the topic branch with fresh commits so it can be remerged
-successfully without needing to "revert the reversion" (see the
-link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
-
 INCOMPATIBLE OPTIONS
 --------------------
 

new file mode 100644
index 0000000000..6e22920a39
@@ -0,0 +1,92 @@
+Directory rename detection
+==========================
+
+Rename detection logic in diffcore-rename that checks for renames of
+individual files is aggregated and analyzed in merge-recursive for cases
+where combinations of renames indicate that a full directory has been
+renamed.
+
+Scope of abilities
+------------------
+
+It is perhaps easiest to start with an example:
+
+  * When all of x/a, x/b and x/c have moved to z/a, z/b and z/c, it is
+    likely that x/d added in the meantime would also want to move to z/d by
+    taking the hint that the entire directory 'x' moved to 'z'.
+
+More interesting possibilities exist, though, such as:
+
+  * one side of history renames x -> z, and the other renames some file to
+    x/e, causing the need for the merge to do a transitive rename.
+
+  * one side of history renames x -> z, but also renames all files within
+    x.  For example, x/a -> z/alpha, x/b -> z/bravo, etc.
+
+  * both 'x' and 'y' being merged into a single directory 'z', with a
+    directory rename being detected for both x->z and y->z.
+
+  * not all files in a directory being renamed to the same location;
+    i.e. perhaps most the files in 'x' are now found under 'z', but a few
+    are found under 'w'.
+
+  * a directory being renamed, which also contained a subdirectory that was
+    renamed to some entirely different location.  (And perhaps the inner
+    directory itself contained inner directories that were renamed to yet
+    other locations).
+
+  * combinations of the above; see t/t6043-merge-rename-directories.sh for
+    various interesting cases.
+
+Limitations -- applicability of directory renames
+-------------------------------------------------
+
+In order to prevent edge and corner cases resulting in either conflicts
+that cannot be represented in the index or which might be too complex for
+users to try to understand and resolve, a couple basic rules limit when
+directory rename detection applies:
+
+  1) If a given directory still exists on both sides of a merge, we do
+     not consider it to have been renamed.
+
+  2) If a subset of to-be-renamed files have a file or directory in the
+     way (or would be in the way of each other), "turn off" the directory
+     rename for those specific sub-paths and report the conflict to the
+     user.
+
+  3) If the other side of history did a directory rename to a path that
+     your side of history renamed away, then ignore that particular
+     rename from the other side of history for any implicit directory
+     renames (but warn the user).
+
+Limitations -- detailed rules and testcases
+-------------------------------------------
+
+t/t6043-merge-rename-directories.sh contains extensive tests and commentary
+which generate and explore the rules listed above.  It also lists a few
+additional rules:
+
+  a) If renames split a directory into two or more others, the directory
+     with the most renames, "wins".
+
+  b) Avoid directory-rename-detection for a path, if that path is the
+     source of a rename on either side of a merge.
+
+  c) Only apply implicit directory renames to directories if the other side
+     of history is the one doing the renaming.
+
+Limitations -- support in different commands
+--------------------------------------------
+
+Directory rename detection is supported by 'merge' and 'cherry-pick'.
+Other git commands which users might be surprised to see limited or no
+directory rename detection support in:
+
+  * diff
+
+    Folks have requested in the past that `git diff` detect directory
+    renames and somehow simplify its output.  It is not clear whether this
+    would be desirable or how the output should be simplified, so this was
+    simply not implemented.  Further, to implement this, directory rename
+    detection logic would need to move from merge-recursive to
+    diffcore-rename.

index 2f47495a4d..a67df4caba 100644
@@ -546,6 +546,38 @@ Other incompatible flag pairs:
  * --rebase-merges and --strategy
  * --rebase-merges and --strategy-option
 
+BEHAVIORAL DIFFERENCES
+-----------------------
+
+ * empty commits:
+
+    am-based rebase will drop any "empty" commits, whether the
+    commit started empty (had no changes relative to its parent to
+    start with) or ended empty (all changes were already applied
+    upstream in other commits).
+
+    merge-based rebase does the same.
+
+    interactive-based rebase will by default drop commits that
+    started empty and halt if it hits a commit that ended up empty.
+    The `--keep-empty` option exists for interactive rebases to allow
+    it to keep commits that started empty.
+
+  * empty commit messages:
+
+    am-based rebase will silently apply commits with empty commit
+    messages.
+
+    merge-based and interactive-based rebases will by default halt
+    on any such commits.  The `--allow-empty-message` option exists to
+    allow interactive-based rebases to apply such commits without
+    halting.
+
+  * directory rename detection:
+
+    merge-based and interactive-based rebases work fine with
+    directory rename detection.  am-based rebases sometimes do not.
+
 include::merge-strategies.txt[]
 
 NOTES

index 6e22920a39..1c0086e287 100644
@@ -90,3 +90,26 @@ directory rename detection support in:
     simply not implemented.  Further, to implement this, directory rename
     detection logic would need to move from merge-recursive to
     diffcore-rename.
+
+  * am
+
+    git-am tries to avoid a full three way merge, instead calling
+    git-apply.  That prevents us from detecting renames at all, which may
+    defeat the directory rename detection.  There is a fallback, though; if
+    the initial git-apply fails and the user has specified the -3 option,
+    git-am will fall back to a three way merge.  However, git-am lacks the
+    necessary information to do a "real" three way merge.  Instead, it has
+    to use build_fake_ancestor() to get a merge base that is missing files
+    whose rename may have been important to detect for directory rename
+    detection to function.
+
+  * rebase
+
+    Since am-based rebases work by first generating a bunch of patches
+    (which no longer record what the original commits were and thus don't
+    have the necessary info from which we can find a real merge-base), and
+    then calling git-am, this implies that am-based rebases will not always
+    successfully detect directory renames either (see the 'am' section
+    above).  merged-based rebases (rebase -m) and cherry-pick-based rebases
+    (rebase -i) are not affected by this shortcoming, and fully support
+    directory rename detection.

new file mode 100755
index 0000000000..8f832957fc
@@ -0,0 +1,105 @@
+#!/bin/sh
+
+test_description='git rebase + directory rename tests'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-rebase.sh
+
+test_expect_success 'setup testcase' '
+	test_create_repo dir-rename &&
+	(
+		cd dir-rename &&
+
+		mkdir x &&
+		test_seq  1 10 >x/a &&
+		test_seq 11 20 >x/b &&
+		test_seq 21 30 >x/c &&
+		test_write_lines a b c d e f g h i >l &&
+		git add x l &&
+		git commit -m "Initial" &&
+
+		git branch O &&
+		git branch A &&
+		git branch B &&
+
+		git checkout A &&
+		git mv x y &&
+		git mv l letters &&
+		git commit -m "Rename x to y, l to letters" &&
+
+		git checkout B &&
+		echo j >>l &&
+		test_seq 31 40 >x/d &&
+		git add l x/d &&
+		git commit -m "Modify l, add x/d"
+	)
+'
+
+test_expect_success 'rebase --interactive: directory rename detected' '
+	(
+		cd dir-rename &&
+
+		git checkout B^0 &&
+
+		set_fake_editor &&
+		FAKE_LINES="1" git rebase --interactive A &&
+
+		git ls-files -s >out &&
+		test_line_count = 5 out &&
+
+		test_path_is_file y/d &&
+		test_path_is_missing x/d
+	)
+'
+
+test_expect_failure 'rebase (am): directory rename detected' '
+	(
+		cd dir-rename &&
+
+		git checkout B^0 &&
+
+		git rebase A &&
+
+		git ls-files -s >out &&
+		test_line_count = 5 out &&
+
+		test_path_is_file y/d &&
+		test_path_is_missing x/d
+	)
+'
+
+test_expect_success 'rebase --merge: directory rename detected' '
+	(
+		cd dir-rename &&
+
+		git checkout B^0 &&
+
+		git rebase --merge A &&
+
+		git ls-files -s >out &&
+		test_line_count = 5 out &&
+
+		test_path_is_file y/d &&
+		test_path_is_missing x/d
+	)
+'
+
+test_expect_failure 'am: directory rename detected' '
+	(
+		cd dir-rename &&
+
+		git checkout A^0 &&
+
+		git format-patch -1 B &&
+
+		git am --3way 0001*.patch &&
+
+		git ls-files -s >out &&
+		test_line_count = 5 out &&
+
+		test_path_is_file y/d &&
+		test_path_is_missing x/d
+	)
+'
+
+test_done

index a67df4caba..9e136ee16e 100644
@@ -563,16 +563,6 @@ BEHAVIORAL DIFFERENCES
     The `--keep-empty` option exists for interactive rebases to allow
     it to keep commits that started empty.
 
-  * empty commit messages:
-
-    am-based rebase will silently apply commits with empty commit
-    messages.
-
-    merge-based and interactive-based rebases will by default halt
-    on any such commits.  The `--allow-empty-message` option exists to
-    allow interactive-based rebases to apply such commits without
-    halting.
-
   * directory rename detection:
 
     merge-based and interactive-based rebases work fine with

index 18ac8226c4..031dbd2ec8 100755
@@ -95,7 +95,7 @@ rebase_cousins=
 preserve_merges=
 autosquash=
 keep_empty=
-allow_empty_message=
+allow_empty_message=--allow-empty-message
 signoff=
 test "$(git config --bool rebase.autosquash)" = "true" && autosquash=t
 case "$(git config --bool commit.gpgsign)" in

index 352a52e59d..81ce9fe7f9 100755
@@ -553,15 +553,16 @@ test_expect_success '--continue tries to commit, even for "edit"' '
 '
 
 test_expect_success 'aborted --continue does not squash commits after "edit"' '
+	test_when_finished "git rebase --abort" &&
 	old=$(git rev-parse HEAD) &&
 	test_tick &&
 	set_fake_editor &&
 	FAKE_LINES="edit 1" git rebase -i HEAD^ &&
 	echo "edited again" > file7 &&
 	git add file7 &&
-	test_must_fail env FAKE_COMMIT_MESSAGE=" " git rebase --continue &&
-	test $old = $(git rev-parse HEAD) &&
-	git rebase --abort
+	echo all the things >>conflict &&
+	test_must_fail git rebase --continue &&
+	test $old = $(git rev-parse HEAD)
 '
 
 test_expect_success 'auto-amend only edited commits after "edit"' '

index cb7c6de84a..da94dddc86 100755
@@ -77,19 +77,14 @@ test_expect_success 'rebase commit with diff in message' '
 '
 
 test_expect_success 'rebase -m commit with empty message' '
-	test_must_fail git rebase -m master empty-message-merge &&
-	git rebase --abort &&
-	git rebase -m --allow-empty-message master empty-message-merge
+	git rebase -m master empty-message-merge
 '
 
 test_expect_success 'rebase -i commit with empty message' '
 	git checkout diff-in-message &&
 	set_fake_editor &&
-	test_must_fail env FAKE_COMMIT_MESSAGE=" " FAKE_LINES="reword 1" \
-		git rebase -i HEAD^ &&
-	git rebase --abort &&
-	FAKE_COMMIT_MESSAGE=" " FAKE_LINES="reword 1" \
-		git rebase -i --allow-empty-message HEAD^
+	env FAKE_COMMIT_MESSAGE=" " FAKE_LINES="reword 1" \
+		git rebase -i HEAD^
 '
 
 test_done

index 0e20a66e73..b2d95e3fb9 100644
@@ -243,11 +243,15 @@ leave out at most one of A and B, in which case it defaults to HEAD.
 --keep-empty::
 	Keep the commits that do not change anything from its
 	parents in the result.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --allow-empty-message::
 	By default, rebasing commits with an empty message will fail.
 	This option overrides that behavior, allowing commits with empty
 	messages to be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --skip::
 	Restart the rebasing process by skipping the current patch.

@@ -271,6 +275,8 @@ branch on top of the <upstream> branch.  Because of this, when a merge
 conflict happens, the side reported as 'ours' is the so-far rebased
 series, starting with <upstream>, and 'theirs' is the working branch.  In
 other words, the sides are swapped.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -s <strategy>::
 --strategy=<strategy>::

@@ -280,8 +286,10 @@ other words, the sides are swapped.
 +
 Because 'git rebase' replays each commit from the working branch
 on top of the <upstream> branch using the given strategy, using
-the 'ours' strategy simply discards all patches from the <branch>,
+the 'ours' strategy simply empties all patches from the <branch>,
 which makes little sense.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -X <strategy-option>::
 --strategy-option=<strategy-option>::

@@ -289,6 +297,8 @@ which makes little sense.
 	This implies `--merge` and, if no strategy has been
 	specified, `-s recursive`.  Note the reversal of 'ours' and
 	'theirs' as noted above for the `-m` option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -S[<keyid>]::
 --gpg-sign[=<keyid>]::

@@ -324,6 +334,8 @@ which makes little sense.
 	and after each change.  When fewer lines of surrounding
 	context exist they all must match.  By default no context is
 	ever ignored.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -f::
 --force-rebase::

@@ -355,19 +367,22 @@ default is `--no-fork-point`, otherwise the default is `--fork-point`.
 --whitespace=<option>::
 	These flag are passed to the 'git apply' program
 	(see linkgit:git-apply[1]) that applies the patch.
-	Incompatible with the --interactive option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --committer-date-is-author-date::
 --ignore-date::
 	These flags are passed to 'git am' to easily change the dates
 	of the rebased commits (see linkgit:git-am[1]).
-	Incompatible with the --interactive option.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --signoff::
 	Add a Signed-off-by: trailer to all the rebased commits. Note
 	that if `--interactive` is given then only commits marked to be
-	picked, edited or reworded will have the trailer added. Incompatible
-	with the `--preserve-merges` option.
+	picked, edited or reworded will have the trailer added.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -i::
 --interactive::

@@ -378,6 +393,8 @@ default is `--no-fork-point`, otherwise the default is `--fork-point`.
 The commit list format can be changed by setting the configuration option
 rebase.instructionFormat.  A customized instruction format will automatically
 have the long commit hash prepended to the format.
++
+See also INCOMPATIBLE OPTIONS below.
 
 -r::
 --rebase-merges[=(rebase-cousins|no-rebase-cousins)]::

@@ -404,7 +421,7 @@ It is currently only possible to recreate the merge commits using the
 `recursive` merge strategy; Different merge strategies can be used only via
 explicit `exec git merge -s <strategy> [...]` commands.
 +
-See also REBASING MERGES below.
+See also REBASING MERGES and INCOMPATIBLE OPTIONS below.
 
 -p::
 --preserve-merges::

@@ -415,6 +432,8 @@ See also REBASING MERGES below.
 This uses the `--interactive` machinery internally, but combining it
 with the `--interactive` option explicitly is generally not a good
 idea unless you know what you are doing (see BUGS below).
++
+See also INCOMPATIBLE OPTIONS below.
 
 -x <cmd>::
 --exec <cmd>::

@@ -437,6 +456,8 @@ squash/fixup series.
 +
 This uses the `--interactive` machinery internally, but it can be run
 without an explicit `--interactive`.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --root::
 	Rebase all commits reachable from <branch>, instead of

@@ -447,6 +468,8 @@ without an explicit `--interactive`.
 	When used together with both --onto and --preserve-merges,
 	'all' root commits will be rewritten to have <newbase> as parent
 	instead.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --autosquash::
 --no-autosquash::

@@ -461,11 +484,11 @@ without an explicit `--interactive`.
 	too.  The recommended way to create fixup/squash commits is by using
 	the `--fixup`/`--squash` options of linkgit:git-commit[1].
 +
-This option is only valid when the `--interactive` option is used.
-+
 If the `--autosquash` option is enabled by default using the
 configuration variable `rebase.autoSquash`, this option can be
 used to override and disable this setting.
++
+See also INCOMPATIBLE OPTIONS below.
 
 --autostash::
 --no-autostash::

@@ -487,6 +510,52 @@ recreates the topic branch with fresh commits so it can be remerged
 successfully without needing to "revert the reversion" (see the
 link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
 
+INCOMPATIBLE OPTIONS
+--------------------
+
+git-rebase has many flags that are incompatible with each other,
+predominantly due to the fact that it has three different underlying
+implementations:
+
+ * one based on linkgit:git-am[1] (the default)
+ * one based on git-merge-recursive (merge backend)
+ * one based on linkgit:git-cherry-pick[1] (interactive backend)
+
+Flags only understood by the am backend:
+
+ * --committer-date-is-author-date
+ * --ignore-date
+ * --whitespace
+ * --ignore-whitespace
+ * -C
+
+Flags understood by both merge and interactive backends:
+
+ * --merge
+ * --strategy
+ * --strategy-option
+ * --allow-empty-message
+
+Flags only understood by the interactive backend:
+
+ * --[no-]autosquash
+ * --rebase-merges
+ * --preserve-merges
+ * --interactive
+ * --exec
+ * --keep-empty
+ * --autosquash
+ * --edit-todo
+ * --root when used in combination with --onto
+
+Other incompatible flag pairs:
+
+ * --preserve-merges and --interactive
+ * --preserve-merges and --signoff
+ * --preserve-merges and --rebase-merges
+ * --rebase-merges and --strategy
+ * --rebase-merges and --strategy-option
+
 include::merge-strategies.txt[]
 
 NOTES

index 40be59ecc4..bf71b7fa20 100755
@@ -20,23 +20,23 @@ onto=!             rebase onto given branch instead of upstream
 r,rebase-merges?   try to rebase merges instead of skipping them
 p,preserve-merges! try to recreate merges instead of ignoring them
 s,strategy=!       use the given merge strategy
+X,strategy-option=! pass the argument through to the merge strategy
 no-ff!             cherry-pick all commits, even if unchanged
+f,force-rebase!    cherry-pick all commits, even if unchanged
 m,merge!           use merging strategies to rebase
 i,interactive!     let the user edit the list of commits to rebase
 x,exec=!           add exec lines after each commit of the editable list
 k,keep-empty	   preserve empty commits during rebase
 allow-empty-message allow rebasing commits with empty messages
-f,force-rebase!    force rebase even if branch is up to date
-X,strategy-option=! pass the argument through to the merge strategy
 stat!              display a diffstat of what changed upstream
 n,no-stat!         do not show diffstat of what changed upstream
 verify             allow pre-rebase hook to run
 rerere-autoupdate  allow rerere to update index with resolved conflicts
 root!              rebase all reachable commits up to the root(s)
 autosquash         move commits that begin with squash!/fixup! under -i
+signoff            add a Signed-off-by: line to each commit
 committer-date-is-author-date! passed to 'git am'
 ignore-date!       passed to 'git am'
-signoff            passed to 'git am'
 whitespace=!       passed to 'git apply'
 ignore-whitespace! passed to 'git apply'
 C=!                passed to 'git apply'

new file mode 100755
index 0000000000..b007a15eba
@@ -0,0 +1,88 @@
+#!/bin/sh
+
+test_description='test if rebase detects and aborts on incompatible options'
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_seq 2 9 >foo &&
+	git add foo &&
+	git commit -m orig &&
+
+	git branch A &&
+	git branch B &&
+
+	git checkout A &&
+	test_seq 1 9 >foo &&
+	git add foo &&
+	git commit -m A &&
+
+	git checkout B &&
+	echo "q qfoo();" | q_to_tab >>foo &&
+	git add foo &&
+	git commit -m B
+'
+
+#
+# Rebase has lots of useful options like --whitepsace=fix, which are
+# actually all built in terms of flags to git-am.  Since neither
+# --merge nor --interactive (nor any options that imply those two) use
+# git-am, using them together will result in flags like --whitespace=fix
+# being ignored.  Make sure rebase warns the user and aborts instead.
+#
+
+test_rebase_am_only () {
+	opt=$1
+	shift
+	test_expect_failure "$opt incompatible with --merge" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --merge A
+	"
+
+	test_expect_failure "$opt incompatible with --strategy=ours" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --strategy=ours A
+	"
+
+	test_expect_failure "$opt incompatible with --strategy-option=ours" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --strategy-option=ours A
+	"
+
+	test_expect_failure "$opt incompatible with --interactive" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --interactive A
+	"
+
+	test_expect_failure "$opt incompatible with --exec" "
+		git checkout B^0 &&
+		test_must_fail git rebase $opt --exec 'true' A
+	"
+
+}
+
+test_rebase_am_only --whitespace=fix
+test_rebase_am_only --ignore-whitespace
+test_rebase_am_only --committer-date-is-author-date
+test_rebase_am_only -C4
+
+test_expect_success '--preserve-merges incompatible with --signoff' '
+	git checkout B^0 &&
+	test_must_fail git rebase --preserve-merges --signoff A
+'
+
+test_expect_failure '--preserve-merges incompatible with --rebase-merges' '
+	git checkout B^0 &&
+	test_must_fail git rebase --preserve-merges --rebase-merges A
+'
+
+test_expect_failure '--rebase-merges incompatible with --strategy' '
+	git checkout B^0 &&
+	test_must_fail git rebase --rebase-merges -s resolve A
+'
+
+test_expect_failure '--rebase-merges incompatible with --strategy-option' '
+	git checkout B^0 &&
+	test_must_fail git rebase --rebase-merges -Xignore-space-change A
+'
+
+test_done